Amorphous SiNx Research Articles

Magnetic patterning of chemically-ordered CrPt3 films

We report magnetic patterning of ferrimagnetic CrPt3 films by locally suppressing the magnetic order using ion-beam irradiation. Chemically-ordered CrPt3 films grown on MgO(110) single-crystal and amorphous SiNx substrates are ferrimagnetic and exhibit strain-induced uniaxial magnetic anisotropy. X-ray diffraction confirms the formation of the L12 phase and magneto-optical Kerr effect spectroscopy reveals the theoretically expected dependence of Kerr rotation and ellipticity on photon energy. Irradiation of the films with 700 keV N+ ions at doses ≳6×1016 ions/cm2 transforms the chemically-ordered CrPt3 ferrimagnetic alloy into the chemically-disordered nonmagnetic fcc phase. As a result, ordered CrPt3 layers can be patterned into magnetic and nonmagnetic regions and are candidate material for ion-beam-patterned magnetic recording media.

Characterization of Silicon Nitride Thin Films on Si and Overlayer Growth of Si and Ge

Crystalline silicon nitride (SiNx) thin films on Si(111) and amorphous SiNx films on Si(001) have been obtained after NH3 or NO exposure at T≈1175 K. The crystallinity of the film on Si(111) has been verified with high-resolution cross-sectional transmission electron microscopy (TEM) and scanning tunneling microscopy. The thickness of the SiNx film is 3–6 atomic layers. When compared with the known phases of Si3N4, our SiNx film is relatively close to β-Si3N4, but it could be a new phase of silicon nitride. Si or Ge forms 3D islands initially when deposited on both crystalline and amorphous SiNx films, and most of the islands are not aligned with the Si substrates. However, on SiNx/Si(111), the islands aligned with the Si substrate grow faster than other islands, so that the overlayer gradually grows into a (111)-oriented columnar film. On SiNx/Si(001), the overlayer films remain polycrystalline in later stages of growth.

Growth of high-quality GaN on Si(111) substrate by ultrahigh vacuum chemical vapor deposition

An ultrahigh vacuum chemical vapor deposition (UHVCVD) system was employed to grow high-quality GaN on a Si (111) substrate using a thin AlN buffer layer. X-ray diffraction, high-resolution electron microscopy (HREM), and photoluminescence (PL) data indicate that a single crystalline GaN layer with a wurtzite structure was epitaxially grown on a silicon substrate. The full width at half maximum (FWHM) of the x-ray rocking curve for the GaN (0002) diffraction was 16.7 arc min. A cross-sectional HREM image showed an amorphous SiNx layer at the Si/AlN interface, as well as stacking faults and inversion domain boundaries in the GaN epilayer. An intense PL emission line, which is associated with the recombination of the donor bound exciton, was observed at 10 K PL spectra (FWHM=6.8 meV) and a strong band edge emission was obtained (FWHM=33 meV) as well, even at room temperature. These results indicate that high-quality GaN can be grown on Si (111) substrates using a UHVCVD growth method.

Physical Properties and Diffusion Characteristics of CVD-Grown TiSiN Films

AbstractTiSiN films grown by chemical vapor deposition were characterized to evaluate the properties relevant to the application as a diffusion barrier in Cu-based interconnects. The films were grown using TiI4 + SiI4 + NH3 + H2 chemistry at substrate temperature, 370°C, and SiI4 - to-TiI4 precursor flow rate ratio of 30. The combined results from x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) revealed that the bulk of Ti32Si21N42 films were predominantly consisted of a mixture of cubic TiN and amorphous SiNx phases. The specific electrical resistivity of the films was about 2000 μΩcm which is a few times higher than that of sputtered TiSiN films having similar composition and thicknesses. The 40 nm-thick barrier appeared to be thermally stable against Cu diffusion at the annealing temperatures up to 550°C. Breakdown of this diffusion barrier occurred at 600°C and was accompanied by the formation of Cu3Si protrusions at the TiSiN/Si interface.

Visible photoluminescence in amorphous SiNx thin films prepared by reactive evaporation

Photoluminescence in the visible domain can be observed in amorphous silicon nitride (a-SiNx) alloys prepared by evaporation of silicon under a flow of nitrogen ions. A strong improvement of the photoluminescence intensity was obtained with annealing treatments in the range 500–1150 °C. Structural investigations were performed by infrared and Raman spectrometry experiments. The optical gap was obtained from transmission measurements in the ultraviolet, visible, and near infrared range. The evolutions of the structure and the optical properties with annealing treatments are correlated to the evolution of the photoluminescence.

Structural properties of AlGaN/GaN heterostructures on Si(111) substrates suitable for high-electron mobility transistors

Transmission electron microscopy (TEM) investigations of metal organic vapor phase deposition grown AlxGa1−xN/GaN heterostructures on Si(111) containing an AlN high-temperature buffer layer have been carried out. The structural properties at the interface and in the epilayer as well as the electronic properties suitable for a high electron mobility transistor (HEMT) were analyzed and compared with systems grown on Al2O3(0001). High resolution TEM (HRTEM) at the AlN/Si(111) interface reveals a 1.5–2.7 nm thick amorphous SiNx layer due to the high growth temperature of TAlN=1040 °C. Therefore, a grain-like GaN/AlN region extending 40–60 nm appears and it is subsequently overgrown with (0001) orientated GaN material because of geometrical selection. The residual strain at the AlN/Si(111) interface is estimated to be εr=0.3±0.6% by Fourier filtering of HRTEM images and a moiré fringe analysis. This indicates almost complete relaxation of the large mismatch f(AlN/Si)=+23.4% which seems to be supported by the SiNx layer. Weak beam imaging and plan view TEM show typical threading dislocations in the epilayer with a density of 3×109 cm−2 extending along 〈0001〉 which sometimes form grain boundaries. An AlxGa1−xN/GaN interface roughness of 3 monolayers is estimated and a small AlxGa1−xN surface roughness of 1.5 nm is obtained by HRTEM and atomic force microscopy investigations which correspond to two-dimensional growth. C–V and Hall measurements reveal two-dimensional electron gas at the Al32Ga68N/GaN interface that has a sheet carrier concentration of 4×1012 cm−2. The electron mobility of 820 cm2/Vs measured at room temperature is applicable for a HEMT grown on Si(111).

イオンビームスパッタリング法によるＴｉＮ／ＳｉＮｘ積層多層薄膜の合成と評価

TiN/SiNx multilayered thin films were deposited on Corning #7059 glass substrates in an ion beam sputtering (IBS) system with a nitrogen assisted ion beam source. The multilayered thin films were deposited alternately using Ti and Si targets sputtered with the argon ion beam. Layer thickness λ (where λ is the period of the multilayer) ranged from 5 to 160 nm, and total film thickness was 400 nm. The multilayered thin films were examined by X-ray diffraction (XRD), cross-sectional scanning electron microscopy (SEM), micro-hardness, and microindentation hardness. Results are as follows : the high angle XRD showed a preferred orientation of TiN to [200] direction and the small angle XRD exhibited a diffraction pattern of a single-crystal superlattice, although the obtained films consisted of multilayers of microcrystal TiN and amorphous SiNx. Hardness of the deposited multilayered thin films indicated maximum against the multilayer periods. The maximum knoop hardness value of the obtained TiN/SiNx multilayered thin film was Hk=2376 kg mm-2.

Compositional analysis of amorphous SiNx: H films by ERDA and infrared spectroscopy

The composition of amorphous SiNx:H films grown by the electron cyclotron resonance (ECR) plasma method was studied by heavy-ion elastic recoil detection analysis (ERDA) with 129Xe ion beams of 1.1 and 1.8 MeV amu−1 and time-of-light (ToF) mass separation. This technique allows simultaneous determination of the absolute atomic concentrations and depth profiles of all involved elements, including hydrogen. Radiation damage at extended ion beam exposure was found to decrease the N/Si ratio and the hydrogen concentration. By measuring the dose dependence, this effect was quantified in order to support correction to zero dose conditions. Monitoring the damage effects by infrared (IR) spectroscopy revealed an increase of the Si–H bond density at the expense of N–H bonds. The results suggest that the damage process is initiated by breaking of N–H bonds and that recapturing of hydrogen by Si appears as an effective competitive process to hydrogen release. Combining the ERDA and IR data, the oscillator strength ratio of the N–H and Si–H stretching bands is found to be 1.4 ± 0.2. Copyright © 2000 John Wiley & Sons, Ltd.

Determination of the possible magnitude of the charging effect in a SCALPEL mask membrane

Previously, we theoretically investigated the charging of free standing dielectric thin films irradiated by 100 keV electrons and formulated kinetic equations describing the dynamic process [M. Mkrtchyan et al., Microelectron. Eng. 46, 233 (1999)]. It was shown that in the currently used SCALPEL® masks comprising a 1000-Å-thick amorphous SiNx film supported by a grillage of Si struts, the membrane charging could be significant and might have an adverse effect on the system performance. The membrane charging, sensitive to both the conductivity and the geometry of conductive path, can be regulated in a straightforward manner by tailoring both of them; for instance, by applying a top surface conductive layer (TSCL) with an appropriate thickness and doping level. Here we discuss the results obtained on the basis of our charging model modified to be applicable to the case of a SiNx membrane with a TSCL (e.g., a 10-nm-thick amorphous Si or poly-Si film doped by boron). The results presented demonstrate that this modification of the membrane is sufficient to avoid the adverse effect of the mask-membrane charging. The required structure can be generated simply by regulating the gas flows in the low-pressure chemical vapor deposition process to produce a thin final layer of a:Si or poly-Si which can be doped during or after deposition.

Titanium Nitride - Silicon Nitride Composite Coatings Deposited by Reactive Magnetron Sputtering

The performance of TiN coatings can be improved by the addition of elements promoting the growth of passive layers. Silicon has been incorporated into TiN during deposition in order to form passivating SiO2 at the surface of the coating. Thin films of Ti-Si-N at thicknesses up to 8 microns have been deposited in a reactive unbalanced magnetron sputter system using a titanium and a silicon target. In contrast to the established coatings containing aluminum or chromium the addition of silicon during the deposition of TiN leads to a multiphase composite deposit with sub-micron sized crystalline TiN embedded in an amorphous SiNx matrix. The addition of small amounts of Si to TiN transforms the (111) oriented columnar structure which develops under typical growth conditions into a dense fine grained structure. The microhardness HV 0.1 of the Ti- Si-N films of about 3500 is significantly higher than the one of Si-free TiN films deposited under the same conditions. The stress states of these films are markedlly enhanced with respect to TiN providing a better wear resistance.

Molecular beam epitaxial growth of AlN single crystalline films on Si (111) using radio-frequency plasma assisted nitrogen radical source

We have grown AlN films on Si (111) using a molecular beam epitaxy (MBE) approach in which reactive nitrogen species are generated in a remote 13.56 MHz radio-frequency plasma discharge, nitrogen radical source. Effects of the Al/Si (111) γ-phase on epitaxial growth of AlN on Si (111) has been studied. Successive processes of forming stable Al/Si (111) γ-phase at 800 °C followed by MBE growth without interrupting Al beam exposure was effective to prevent amorphous SiNx formation on Si substrate. The Al/Si (111) γ-phase was found effective to fix the orientation relationship between AlN and Si for epitaxial growth of single crystal AlN. Single crystal AlN was grown on the Al/Si (111) γ-phase at the temperature as low as 400 °C. By optimizing growth conditions (substrate temperature, V/III ratio and plasma conditions), growth of single crystal AlN films in a quasi-layer-by-layer fashion was observed for the thickness up to 60 nm. The optimized value on the growth temperature was 800 °C and that on the V/III ratio was 440. The surface of the AlN film grown under the optimized condition was quite smooth with a root mean square roughness of 0.3 nm. The resistivity of the film was about 2×109 Ω cm.

Bonding structure and characteristics of defects of near-stoichiometric silicon nitride films

Amorphous SiNx:H films having nitrogen content x greater than 1.3 were deposited at 300 °C by varying the ammonia-to-monosilane flow-rate ratio RN, using plasma-enhanced chemical- vapor-deposition. The characteristics of defects in the films subjected to UV illumination and anneal treatments were investigated by electron-spin-resonance (ESR) measurements. The paramagnetic Si dangling bonds (DBs) with three N atom neighbors, called the K0 center, were observed for an as-deposited film with RN of 5, and the density was favorably enhanced by exposing the film to UV light or by the UV illumination subsequent to its annealing. The K0 density decreased as the film was annealed at 550 °C after the UV illumination. The mechanisms of creation and disappearance of the K0 centers by the illumination and the annealing, respectively, were interpreted in terms of the potential fluctuation model. The K0 density in as-deposited films decreased with RN, and a new three-line spectrum was observed as RN exceeds 7. Origins of this new spectrum are discussed. The ESR spectra due to N DBs were observed for only the films subjected to the anneal/illumination sequence, and the densities of both N DBs and K0 centers decreased with increasing the annealing time before the illumination.

Structural Study of Amorphous SiNx:H Films Produced by Plasma-Enhanced Chemical Vapor Deposition

The structure of amorphous SiNx:H films prepared by glow discharge decomposition of SiH4 and NH3 has been investigated by measurements of X-ray diffraction intensity. The first peak in atomic density function obtained by analysis of diffraction intensity indicates a nearest-neighbor distance of 1.74 Å which corresponds to the Si–N bond length of 1.730–1.745 Å in β-Si3N4 crystal. We have also estimated the Si–N–Si–N bond configuration by comparing the corrected observed scattering intensity with the scattering intensity calculated using a simple bonding model. It has been shown that a Si atom bonded to a N atom with a coplanar bond has two tetrahedral bonds in the plane of the coplanar bonds.

Analysis of Reaction at Au/Si<sub>3</sub>N<sub>4</sub> Interface by XPS-SIMS

Interface reaction between Au film and single-crystal α-Si3N4 was analyzed with depth profile by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). Diffusion of Si from the Si3N4 to the Au film surface was observed by SIMS. Clear evidence which indicates low-temperature (600°C) solid reaction between Au and Si3N4 was also observed. The interface region exhibited peaks corresponding to Au-Si bond, Si-N bond and dangling nitrogen bond in the XPS spectra. It is considered that the Au-Si bond was formed by dissociating Si-N bond, and the reaction mechanism is similar to Au-Si reaction at Au/Si in-terface. In the case of Au and amorphous SiNx, the interface reaction was more remarkable than that of the single-crystal Si3N4.

Determination of local structure using X-ray emission spectroscopy: hydrogenated a-SiNx and a-SiOx

It is demonstrated that, by a detailed analysis of the X-ray emission bands for hydrogenated amorphous SiNx and SiOx alloy films, it is possible to distinguish between the local structure described by the random-bond and random-mixture models.

Metalorganic chemical vapor deposition growth of InN for InN/Si tandem solar cell

A new tanden solar cell having an InN top cell is proposed since InN is a binary material having a bandgap of about 1.9 eV suitable for a top cell in a 2-junction tandem cell. An estimation of the conversion efficiency of InN/Si tandem cell has been made. For a 2-terminal cell, the bandgap of InN, 1.95 eV, is close to the optimum for AM 0 illumination because currents between top and bottom cells can be matched. The MOCVD growth of InN has been studied as a key technology for device fabrication. Epitaxial growth of InN directly on Si using the MOCVD technique is unsuccessful because of the formation of an amorphous SiNx layer on the Si substrate surface. Characterization has been made for single-crystalline InN films grown on α-Al2O3 substrates. Compared with InN films grown at a reduced pressure (≈ 76 Torr), those grown at the atmospheric pressure have a lower background carrier concentration and a higher electron mobility, although thier surface morphology and crystallographic quality are somewhat worse.

Effects of active hydrogen on the stress relaxation of amorphous SiNx:H films

Amorphous SiNx:H (a-SiNx:H) films were deposited at 300 °C by plasma-enhanced chemical vapor deposition using SiH4–NH3–H2 mixtures. The stress, vibrational absorption, buffered HF (BHF) etch rate, and breakdown strength were investigated as a function of the gas volume ratio [H2]/[SiH4](=RH) and rf power. The [NH3]/[SiH4] ratio was maintained at 10, in which nitride films having a near-stoichiometric composition can be obtained. The measured stress for these films was intrinsic stress. It was suggested that the stress is relaxed by forming Si—NH—Si bonds instead of N—Si3 bonds. An increase in both RH and rf power values was found to decrease the stress and BHF etch rate and increase the breakdown strength. A change in the bonding structure with increasing RH and rf power is examined in terms of a thermodynamic equilibrium reaction, and it was suggested that increased H* radicals and/or H+ ions play an active role in relaxing the stress through the structural change.

Effects of annealing ZnO films prepared by ion-beam-assisted reactive deposition

Annealing ZnO films prepared by ion-beam-assisted deposition (IBAD) in air above 773 K can change the resistivity from ≈10−4Ω cm to more than 106Ω cm, changing the films from a highly degenerate transparent material to a thermally activated semiconductor. No change in the transmission through the visible region of the spectrum (more than 90%) is observed but the optical band gap can change from ≈3.41 to ≈3.24 eV, as a result of a Burstein-Moss shift. However, for films that are not initially very transparent, the average transmission can be increased from ≈28% to more than 85%. High temperature annealing increases the average size of crystallites by ≈15%. After annealing, a large photoresponse is observed, with the conductivity increasing by more than a factor of 105 when the film is illuminated with UV light (≈4 × 1016 photons cm−2 s−1). The rise and decay time constants are very large, indicating that previously reported surface structural changes occur. These constants strongly depend on the intensity of the light and the ambient gases present. Any true photoconductivity present appears to be very small. Encapsulating the free surface of a ZnO film with a layer of amorphous SiNx can help to stabilize the film, and it decreases the photoresponse time as well as the magnitude of the photoresponse.

Analysis of local structure in amorphous SiNx:H alloy films in terms of x-ray emission spectroscopy

We present Si K- and Si L-emission bands of amorphous SiNx:H alloy films (0 ⩽ x ⩽ 2) prepared by plasma deposition at low power. We discuss the photon energy positions of spectral features in the Si K- and Si L-emission bands in view of the random-bonding model (RBM) and the random-mixture model (RMM) of local structure. We show that the observed spectra favour RMM over RBM for our samples.

Electronic structure of amorphous Si-N compounds

The authors report results of experiments of valence band (VB) photoemission and dark conductivity of amorphous SiNx:H (0<or=x<1.5). The most important change observed in the electronic structure when x increases is the replacement of Si-Si bonding states at the top of the VB by Si-N bonding states at the centre of the band. A plot of the band edges is presented which shows that the sudden opening of the gap at x approximately=1 is due mainly to the recession of the conduction band minimum.